Add support for SDL groups
SDL group is an unordered collection of members where each member is
unique.
Add the following methods to do operations with groups:
-AddMember: adds number of members into a given group. It is possible to
give already existing members to be added but that doesn't have an
effect to group.
-RemoveMember: Remove number of members from a group. It is possible to
try to remove non-existing members from a group without an error.
-RemoveGroup: Remove the whole group along with its members.
-GetMembers: Get all members from a group.
-IsMember: Check if a specific member is part of the group.
-GroupSize: Return the number of members in group.
Change-Id: I9005ffe584aa0872c5a3fab170d0ac37d9b9f30a
Signed-off-by: Marco Tallskog <marco.tallskog@nokia.com>